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--------------------------------------------------------------------------------
-- | Internal module to parse metadata
{-# LANGUAGE BangPatterns #-}
{-# LANGUAGE RecordWildCards #-}
module Hakyll.Core.Provider.Metadata
( loadMetadata
, parsePage
, MetadataException (..)
) where
--------------------------------------------------------------------------------
import Control.Arrow (second)
import Control.Exception (Exception, throwIO)
import Control.Monad (guard)
import qualified Data.ByteString as B
import qualified Data.ByteString.Char8 as BC
import Data.List.Extended (breakWhen)
import qualified Data.Map as M
import Data.Maybe (fromMaybe)
import qualified Data.Text as T
import qualified Data.Text.Encoding as T
import qualified Data.Yaml as Yaml
import Hakyll.Core.Identifier
import Hakyll.Core.Metadata
import Hakyll.Core.Provider.Internal
import System.IO as IO
import System.IO.Error (modifyIOError, ioeSetLocation)
--------------------------------------------------------------------------------
loadMetadata :: Provider -> Identifier -> IO (Metadata, Maybe String)
loadMetadata p identifier = do
hasHeader <- probablyHasMetadataHeader fp
(md, body) <- if hasHeader
then second Just <$> loadMetadataHeader fp
else return (mempty, Nothing)
emd <- case mi of
Nothing -> return mempty
Just mi' -> loadMetadataFile $ resourceFilePath p mi'
return (md <> emd, body)
where
normal = setVersion Nothing identifier
fp = resourceFilePath p identifier
mi = M.lookup normal (providerFiles p) >>= resourceInfoMetadata
--------------------------------------------------------------------------------
loadMetadataHeader :: FilePath -> IO (Metadata, String)
loadMetadataHeader fp = do
fileContent <- modifyIOError (`ioeSetLocation` "loadMetadataHeader") $ readFile fp
case parsePage fileContent of
Right x -> return x
Left err -> throwIO $ MetadataException fp err
--------------------------------------------------------------------------------
loadMetadataFile :: FilePath -> IO Metadata
loadMetadataFile fp = do
fileContent <- modifyIOError (`ioeSetLocation` "loadMetadataFile") $ B.readFile fp
let errOrMeta = Yaml.decodeEither' fileContent
either (fail . show) return errOrMeta
--------------------------------------------------------------------------------
-- | Check if a file "probably" has a metadata header. The main goal of this is
-- to exclude binary files (which are unlikely to start with "---").
probablyHasMetadataHeader :: FilePath -> IO Bool
probablyHasMetadataHeader fp = do
handle <- IO.openFile fp IO.ReadMode
bs <- BC.hGet handle 1024
IO.hClose handle
return $ isMetadataHeader bs
where
isMetadataHeader bs =
let pre = BC.takeWhile (\x -> x /= '\n' && x /= '\r') bs
in BC.length pre >= 3 && BC.all (== '-') pre
--------------------------------------------------------------------------------
-- | Parse the page metadata and body.
splitMetadata :: String -> (Maybe String, String)
splitMetadata str0 = fromMaybe (Nothing, str0) $ do
guard $ leading >= 3
let !str1 = drop leading str0
guard $ all isNewline (take 1 str1)
let !(!meta, !content0) = breakWhen isTrailing str1
guard $ not $ null content0
let !content1 = drop (leading + 1) content0
!content2 = dropWhile isNewline $ dropWhile isInlineSpace content1
-- Adding this newline fixes the line numbers reported by the YAML parser.
-- It's a bit ugly but it works.
return (Just ('\n' : meta), content2)
where
-- Parse the leading "---"
!leading = length $ takeWhile (== '-') str0
-- Predicate to recognize the trailing "---" or "..."
isTrailing [] = False
isTrailing (x : xs) =
isNewline x && length (takeWhile isDash xs) == leading
-- Characters
isNewline c = c == '\n' || c == '\r'
isDash c = c == '-' || c == '.'
isInlineSpace c = c == '\t' || c == ' '
--------------------------------------------------------------------------------
parseMetadata :: String -> Either Yaml.ParseException Metadata
parseMetadata = Yaml.decodeEither' . T.encodeUtf8 . T.pack
--------------------------------------------------------------------------------
parsePage :: String -> Either Yaml.ParseException (Metadata, String)
parsePage fileContent = case mbMetaBlock of
Nothing -> return (mempty, content)
Just metaBlock -> case parseMetadata metaBlock of
Left err -> Left err
Right meta -> return (meta, content)
where
!(!mbMetaBlock, !content) = splitMetadata fileContent
--------------------------------------------------------------------------------
-- | Thrown in the IO monad if things go wrong. Provides a nice-ish error
-- message.
data MetadataException = MetadataException FilePath Yaml.ParseException
--------------------------------------------------------------------------------
instance Exception MetadataException
--------------------------------------------------------------------------------
instance Show MetadataException where
show (MetadataException fp err) =
fp ++ ": " ++ Yaml.prettyPrintParseException err ++ hint
where
hint = case err of
Yaml.InvalidYaml (Just (Yaml.YamlParseException {..}))
| yamlProblem == "mapping values are not allowed in this context" -> "\n" ++
"Hint: if the metadata value contains characters such\n" ++
"as ':' or '-', try enclosing it in quotes."
Yaml.AesonException "Error in $: parsing HashMap ~Text failed, expected Object, but encountered String"
-> "\nHint: in metadata, keys and values are separated by a colon *and* a space."
_ -> ""
|
